The invention relates to a decanter centrifuge of the type having a scroll conveyor rotatable around a preferably horizontal axis of rotation mounted substantially concentrically within a rotating bowl.
Such systems are known from, e.g., U.S. Pat. No. 5,403,486. The system features scroll conveyor with a scroll hub including an inside surface and an outside surface, at least one passageway between the inside surface and the outside surface and a feed pipe in the center of the hub. A number of extensions form a multispray nozzle. This patent presents a rotating wash feed compartment to improve cake washing and an acceleration system of the feed by using U-shaped channels extending from the inside to the outside surface of a conveyor hub. The U-shaped channel communicates with an inwardly extending L-shaped baffle which opposes the Coriolis force. This design creates sudden feed acceleration by breaking particles or flocs and product accumulation behind baffles by reducing its effect quickly. The U-shaped channels extending to the outside of the conveyor has disadvantages in that the feed slurry is discharged in the pool in the form of concentrated jets which results in a remixing of already separated solids. As these channels are not filled full with liquid the air circulation is not well controlled because these kind of channels work as a fan by putting air under pressure. These systems are very complex and also tend to clog when a more sticky suspension is fed in.
US 2014/0005024 discloses a new feed chamber provided with a proximal cross wall, distal cross wall and wear resistance members which are extend on the all inner surface of the feed chamber. U.S. Pat. No. 3,568,920 presents a dismountable insert concerning a feed chamber for wear resistance. The raw materials are fed into the machine through a rotating feed pipe in a bushing feed chamber. The scroll is provided with an inner rotor fixed with bolts on the outside of scroll conveyor. It is possible to disassembly the inner rotor in order to change the bushing inserts. This scroll is complex to manufacture, the rotating feed pipe is difficult to seal and the nozzles of the feed chamber are not extended inside and outside of the feed chamber.
DE 40 41 868 shows a centrifuge with an insert for all the inside surface of the feed chamber made in one part for wear resistance. This cannot be replaced and this after this insert is worn the whole centrifuge scroll has to be dismantled and refurbished.
U.S. Pat. No. 5,380,266 shows a feed accelerator system with vanes inside a conical feed chamber is presented. This system improves the efficiency of the feed chamber by accelerating the product inside the feed chamber at the rotational speed of the scroll before to discharge in the pool of the centrifuge. Another accelerating system inside the feed chamber is presented in the U.S. Pat. No. 5,401,423.
A traditional decanter runs at high speed and the feeding of the machine is at zero rotational speed of the product. One of the difficulties is to bring the feed at the bowl speed with high efficiency, low shear rate (smooth acceleration to avoid breaking of particles or flocs) and without having important wear. During operation of a centrifuge wear may occur inside of the feed chamber and at the discharge ports. It is often necessary to carry out a cut of the scroll, a new welding and new balancing. Standard feed chambers are made for high hydraulic efficiency or wear protection or easy maintenance but not all these futures in the same time.